Anything of value is melted down and sold on by the company who 'trash' the aircraft. Key fluids are recycled. I believe airlines have a recycling method as well for maintenance aka anything which is expensive to buy, but can be reused will be given back to them for use in the future.
The alloys etc are sold onto whoever needs it. There are many rare metals in modern aircraft that are put to use in the making and maintenance of craft.
This is my limited knowledge.